ACT English: Use Which vs. That Correctly for Nonrestrictive Clauses

That introduces a restrictive clause (no comma): information essential to identifying the noun. Which introduces a nonrestrictive clause (with comma): extra information about an already-identified noun. Example: "The car that I bought last year is reliable" (restrictive: which car? the one I bought). "My car, which I bought last year, is reliable" (nonrestrictive: we know which car; I'm adding extra info). If the clause is essential, use that. If it's extra, use which with commas.

Test yourself: "The books that are on the shelf are mine" (essential—which books? those on the shelf). "My books, which are on the shelf, are mine" (extra—you already know my books). The same sentence with that or which changes meaning, so getting this right matters.

Error 1: Using which without commas: "The movie which won the award was excellent" (wrong). Fix: "The movie that won the award was excellent" (no commas = restrictive = use that). Error 2: Using that with commas: "The movie, that won the award, was excellent" (awkward and wrong). Fix: "The movie, which won the award, was excellent" (commas = nonrestrictive = use which). On ACT English, if you see which without commas or that with commas, that answer is usually wrong.

When in doubt, ask: Is this clause essential (answers "which one?") or extra (just adding detail)? Answer that question and you'll pick the right word and punctuation.

(1) "The student which studied hard passed the test" → (2) "The students, that scored well, received scholarships" → (3) "My phone that I bought yesterday, works great" → (4) "Paris, that is in France, is beautiful" → (5) "The rule which governs the club is strict." Correct each sentence by choosing that or which and adding/removing commas as needed. If you correct all five correctly, you've mastered this skill.

Answers: (1) "...that studied hard..." (2) "...which scored well..." (3) "...that I bought yesterday works great" (no commas). (4) "Paris, which is in France, is beautiful." (5) "The rule that governs the club is strict" (no commas). Compare your answers to these and identify your pattern of error, if any.

Which vs. that questions appear on most ACT English tests. This is a straightforward grammar rule with no ambiguity: restrictive=that, nonrestrictive=which. Memorizing this single distinction and its punctuation rules earns you 1-2 points per test.

Spend 10 minutes memorizing the rule and drilling the five sentences above. By test day, you'll automatically choose the correct word and punctuation, adding free points to your English score.